Elevated levels of prostaglandins (PG) have been found in inflammed gingival tissues. Since some of the effects of PG mimic the characteristics encountered in periodontal disease, it has been postulated that there is a direct relationship between PG levels and periodontal disease. The proposed studies are designed to determine whether the availability of PG precursors and the synthesis of PG can be influenced by microorganisms present in the gingival crevice and periodontal pockets. Microorganisms commonly found in supra-/or subgingival plaque or in the gingival crevice, and microorganisms isolated from humans with periodontosis, periodontitis and Papillon-Lefevre Syndrome will be studied. The objectives are two fold: a) to determine the ability of bacteria to synthesize extracellular phospholipase A (PL-A) and presumably to release PG precursors from gingival cell membranes; b) to identify microorganisms that may synthesize PG-like substances. Crude enzyme extracellular preparations will be screened for PL-A activity by monitoring the release of lysocompounds from labelled lecithin. Thin layer chromatography and liquid scintillation counting of reaction products will be used to demonstrate enzymic activity. The ability of enzyme preparations to release PG precursors from epithelial tissue cultures obtained from explants of experimental animals will also be monitored. Thin layer chromatography and gas liquid chromatography with appropriate standards will be used for this purpose. The screening of bacteria for the synthesis of PG-like substances will be performed by following the conversion of 3H-Arachidonate to substances that co-chromatograph with known PG's. Radioimmunoassays will be used for quantification and PG-like substances will be assayed for their ability to promote fetal bone resorption in vitro. Purification of bacterial PL-A will be attempted in order to study their effect in vitro on gingival fragments or in vivo for the assessment of histopathological changes produced by subgingival injections into experimental animals.